Field of the Invention
The invention relates to web drive systems, and more particularly to direct reel-to-reel web transports which have no web length buffering means to decouple web motion at the head from web motion at the reels.
Transports for web-like material, such as magnetic recording tape, in the past have been mainly characterized as buffered or unbuffered. In a buffered transport, tape is delivered from the supply reel to a mechanical buffer or a vacuum column buffer to decouple the tape motion at a drive capstan from the supply reel. The drive capstan drives the tape over a read/write recording head to another buffer which decouples the tape from a take-up reel. From the second buffer, the tape is wound upon the take-up which is driven by a take-up reel motor. These systems tend to be very expensive and therefore a simpler type of system wherein the tape is unbuffered has been employed. In an unbuffered system, the tape extends from the supply reel to the take-up reel past the read/write station. The speed, position and tension of the tape as it passes through the read/write station must be accurately controlled and this is done by controlling the two reel motors.
In prior apparatus, the control of the motors is accomplished by two tape tension sensors, one on each side of the tape head. Alternatively, the speed of the take-up capstan is controlled from a recording head which senses a prerecorded track on the tape. Or in still other prior art devices, a tape speed tachometer controls one reel motor and a tape tension transducer controls the other reel motor.
None of the above systems are truly adaptive in that they lack the total ability to maintain predetermined control objectives dynamically as the amount of tape on each reel changes with time. This is especially important when controlling large diameter tape reels which exhibit a significant change of tape reel radius during operation.
It is therefore an object of this invention to provide a reel-to-reel web transport system which is of low cost and high reliability.
It is a further object of this invention to provide an adaptive reel-to-reel web control system which is capable of maintaining predetermined control parameters as the amount of tape on each reel changes with time.
It is a further object of this invention to provide a web motion control system in which equal tangential motion trajectories are maintained for each reel.
A further object of this invention is to provide a web control apparatus which maintains equal tensioning forces on a web driven directly from reel-to-reel.
Another object of the invention is to provide a tape motion control apparatus which provides a closed loop high-speed rewind and forward search.